Here are the steps I used. First, go grab the coolbits.reg file
from here
coolbits.reg.
Scroll down the page until you get see the coolbits reference.
Then, make sure you are using the nVidia reference drivers. I was using
5.22, but I think anything above 5.00 works.
Once you have the reference drivers loaded, you should see a tab in
the display properties for your card (I had one called GeForce 256, and
then NV11 when I upgraded to a GF2 MX). Select that tab, and select
additional properties. With the coolbits registry hack, you should see
a tab called "hardware properties". Click that, select "enable hardware
adjustment", or whatever that check box is called. Let it reboot, and then
you can use the sliders to overclock the card.
You can apparently also get some other overclocking/bios moding utilities
here
http://zoiah.m3dzone.com
HTH